A current attitude determination system is disclosed in U.S. Pat. No. 5,296,861, showing a flat, triangular antenna array mounted horizontally level in the frame of reference of a selected vehicle. U.S. Pat. No. 5,296,861 is expressly referenced and incorporated herein in its entirety. The antenna array of this U.S. patent may be installed on a plate, which in turn may be mounted on a television antenna rotor. The antenna array includes first and second antenna baselines between a reference antenna and selected first and second other antennas. This patent recites a method at column 22, line 3, of:
"determin[ing] . . . the range of integers that are possible for the first baseline, given only the known constraints on vehicle roll and pitch . . . " PA1 "calculat[ing] . . . the arc of coordinates that are possible for the second antenna, assuming that the first antenna coordinate is true . . . [and determining] the range of integers that are possible for the second baseline"
For satellites nearly overhead, only a small range of integers is possible if the vehicle is constrained from significant rolling and pitching. In particular, U.S. Pat. No. 5,296,861 shows step (f) at column 22, line 22, including
The flat antenna array method patented, however, cannot operate, if the array is mounted in three dimensions rather than in the plane of the vehicle which carries it. The methodology of the invention requires users of the attitude determination systems to attach antennas at selected points of a vehicle which are not likely to be aligned with the plane of the transporting vehicle. Instead, the points of attachment of the antennas on the vehicle are likely to be out-of-plane. On aircraft, a common configuration is to mount two antennas on the fuselage, and two more out on wings, producing substantial slope between antenna axes and the vehicle-level frame of reference. Accordingly, the vehicle carrying the antennas can have any azimuth between 0 and 360 degrees, and it can tilt in any direction about level up to some maximum angle, such as 15 degrees, but, notably, this range of motion pertains to the vehicle, not to the antenna sites.
According to a current approach, the antennas are mounted in flat, planar arrays in the vehicle frame of reference, leading to a particular solution for determining the range of possible carrier cycle integers. However, for antennas that are substantially out-of-plane, no method for determining the range of integers is known to be in use.
It is accordingly desirable to develop a system and method for attitude determination which is not dependent upon co-planarity of antenna disposition with the plane of the vehicle on which the antennas are mounted.